The present invention generally relates to magnetic field sensing and, more particularly, is related to a system and method for providing a resonant micro-compass that is capable of detecting the Earth""s magnetic field, while consuming minimal power.
For centuries the compass has provided an easy and inexpensive means of determining proper direction of travel. Even though people in earlier times did not understand the phenomenon of magnetic field interaction, they noticed the polarity of magnets and the action that the Earth""s magnetic field produced on it. They were able to develop a very simple instrument consisting of a small, lightweight magnet, such as a needle, balanced on a nearly frictionless pivot point, which displayed the direction of the magnetic North at the point of observation. Generally, a compass is simply a magnetic field sensor that can determine the horizontal component of the Earth""s magnetic field.
A large number of magnetic sensors exist which are based on different physical effects such as the Hall effect, the Zeeman effect and/or the magnetoresistive effect, that can either be used to measure the intensity of a magnetic field, or its direction. Magnetic sensors have assisted in the analyzing and controlling of many functions for many decades. These magnetic sensors vary in size, performance, complexity (from simple Vibrating Sample Magnetometers to Superconducting Quantum Interference Device (SQUID) Magnetometers), and field of application (such as brain function mapping, magnetic anomaly detection, mineral prospecting, non-contact switching, current measurement or magnetic readout memory).
However, few magnetic sensors such as search-coil magnetometers, flux-gate magnetometers or magnetoresistive magnetometers, and giant magnetoresistive field sensors, can be used as a compass of a relatively small size, such as within the millimeter or centimeter scale, that does not need a high power supply or a complicated and costly way to operate. Some companies provide small magnetic compasses, such as the Digital Magnetic Compass, by Leica, and the HMR 3000, by Honeywell, that are centimeter scale solid state sensors that require about a ten mA power supply. Unfortunately, even if research is performed to improve conventional existing systems, or find new and interesting ways to make compasses, those devices are still too large and/or consume too much power to be used in low-power and micro-scale applications. Such applications may include, but are not limited to, use within a wristwatch.
The present invention provides a resonant micro-compass for detecting the Earth""s magnetic field while requiring minimal power.
Generally, in architecture, the micro-compass comprises a resonant structure that is driven at its resonant frequency. The resonant frequency of the resonant structure is then measured. A magnet is located on the resonant structure such that introduction of a magnetic field, such as the Earth""s magnetic field, to the micro-compass causes a reaction by the magnet which, in turn, causes the resonant frequency of the resonant structure to shift. This shift of resonant frequency is then measured, thereby allowing the micro-compass to detect the direction of the magnetic field with extreme accuracy.
The invention also provides a method for determining the direction of the Earth""s magnetic field while using a micro-compass that utilizes minimal power. The method can be summarized by the steps of resonating a resonant material wherein the resonating material has magnetic properties that enable the resonating material to resonate; measuring the resonant frequency of the resonating material; subjecting the resonating material to a magnetic field; and measuring a shift in the resonant frequency of the resonating material where the measurement is indicative of the angle between the magnetic field and the micro-compass and allows the micro-compass to detect the direction of the magnetic field.
The invention has numerous advantages, a few of which are delineated hereafter as examples. Note that the embodiments of the invention, which are described herein, possess one or more, but not necessarily all, of the advantages set out hereafter.
One advantage of the invention is that it provides a micro-scaled magnetic field sensor that consumes very low power.
Another advantage is that while it is capable of detecting the Earth""s magnetic field, it is also small enough to enable use in many applications.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the accompanying claims.